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Qns:-Three dimensional packing in solids (12th chemistry)
Answers
Answer:
Tetrahedral void:- A simple triangular void like c in crystal is surrounded by four spheres and is called a tetrahedral void. ... Now when a third layer placed over second layer in such a way that sphere cover the tetrahedral (c) void a three dimensional close packing of ABAB patter or hexagonal close packing is obtained.
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Answer:
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n this kind of close solid packing, the second layer is placed over the first layer in such a way that the spheres of the upper layer are exactly above those of the first layer. In other words, spheres of both the layers are perfectly aligned, horizontally as well as vertically. Let us name the arrangement of spheres in the first layer as ‘A’ type since all the layers have the same arrangement, the lattice can be observed to follow AAA…. type pattern. This kind of lattice is better known as a simple cubic lattice.
Three-dimensional close packing from two-dimensional hexagonal close-packed layers:
The three-dimensional close-packed structure can be generated by placing layers one over the other.
Placing the second layer over the first layer:
In this kind of close packing, a second layer similar to the below layer is placed in such a way that the spheres of the second layer are placed in the depressions of the first layer.Since the spheres of the two layers are aligned differently, if the first layer is termed as ‘A; the second layer can be termed as ‘B’. We notice that a tetrahedral void is formed wherever a sphere of the second layer is above the void of the first layer (or vice versa). Whereas at other places, we observe that the triangular voids in the second layer are above the triangular voids in the first layer, such that the triangular shapes of these do not overlap. Such voids are known octahedral voids and are surrounded by six spheres.
We can easily calculate the number of these two types of voids. Let the number of close packed spheres be N, then:
The number of octahedral voids generated = N
The number of tetrahedral voids generated = 2N
Placing the third layer over the second layer:
There are two prominent ways in which the third layer can be placed over the second layer: